1. Field of the Invention
The present invention relates to a system for the bidirectional optical transmission of information. In particular, it relates to the connection of electronic components via a bidirectional optical bus system.
2. Description of the Related Art
Electronic systems are normally composed of a series of fixed and/or variable electronic components (subsystems), which are connected to one another by a bus, which transports signals from one component to another.
Thus digital computer systems for example are designed in this way. A number of individual cards or electronic components form subsystems, which are integrated into a bus system, which transports signals for data, storage addresses, interrupts and the like. One of these cards may carry a processor for the execution of application programs, while others in turn may contain controllers for workstations or displays, adapters for mass storage units or interfaces for LANs (Local Area Networks) etc. However, the subsystems can also comprise navigation units, e.g. for use in cars, and video/audio or remote control units.
The functional electronic circuits on the individual cards or components have access to the common bus system for the transmission of data, addresses and control signals according to a certain bus protocol.
This type of packaging has important advantages. Thus a varying number of different types of subsystems can be configured in the system as a whole, for example. Adaptation of the system to the respective user environment is simple and can often be undertaken by the user without further assistance. New functions and improved technology can be integrated without difficulty at a later date without having to replace the entire system. Furthermore, diagnosis and repair of the system are improved by isolating individual subsystems.
Conventional hard-wired bus systems are relatively expensive and have disadvantages. In so far as electronics technology is experiencing increasing integration, connectors for transmitting signals from one unit to another are becoming ever more expensive or reliability can only be achieved at a very high cost. Added to this is an ever greater space requirement
Some suggestions have been made for replacing parallel hard-wired (xe2x80x9ccopperxe2x80x9d) backplane bus systems for connecting individual subsystems of an electronic system, especially in the field of optical technologies. In spite of the necessity of converting electrical high-speed signals into optical signals and vice-versa, several optical backplane bus systems have been proposed. However, in this process optical signals are still only transmitted from one special point to another special point inside optical fibres. The biggest problem appears to lie in the fact that proposed optical bus systems, which could perhaps be used to connect a large number of electronic components, are very much more expensive and are only to be made as reliable as the hard-wired bus systems they are intended to replace at considerable expense. Exotic optical components, precise alignment within the components and the size of the optical units have caused the application of optical technologies to fail in electronic systems in which a large number of components have to communicate with one another via a common bus system.
It is also known to use light communications systems for serial and/or parallel communication, for example infrared systems in the case of light distribution in open spaces with air as the medium (remote controls) or laser light systems via optical fibres.
However, these systems have the disadvantage that either mutual interference restricts the application to so-called half-duplex operation, signals only being able to be transmitted simultaneously in one direction (IR remote control), or optical fibres or glass-fibre cables are used, which are susceptible to faults, can only be rendered operational using expensive plug-in systems and with regard to which problems occur in the transition of light between the cable and the plug-in connection (plug), for example due to condensation (laser light systems).
U.S. Pat. No. 5,113,403 and U.S. Pat. No. 5,209,866 disclose an electronic system consisting of a number of subsystems or electronic components, which are connected by an optical bus. The individual electronic components are arranged in a housing in such a manner that optical interface units disposed on each component form a monoaxial, bidirectional optical bus working in free space which distributes electrical signals among the individual components. These signals are transmitted along a single linear axis as polarized light beams. Here each individual component has a bus interface unit for generating outgoing light beams and receiving incoming beams along both directions of the axis respectively. The interface units use laser generators, photodetectors and amplitude-beam-splitters.
In spite of an improvement in the technique, however, these systems are still cost-intensive and only allow for compact construction to a very limited extent, since each individual component requires optical interface units.
Furthermore, these systems display lower reliability on account of the large number of optical elements used.
The object of the present invention is therefore to provide a system for the bidirectional optical transmission of information which utilizes,the advantages of optical technologies on the one hand and is economical on the other hand, displays a high degree of reliability in relation to faults and also permits compact construction of the individual electronic components.
This object is achieved according to the invention by a system for the bidirectional optical transmission of information with the aid of diffuse light between several electronic components with n transmission links.
In the system according to the invention, sheathing is provided for at least (nxe2x88x921) transmission links in such a manner that mutual obstruction of the individual transmission links is prevented. In this regard a single transmission link can be formed as a so-called xe2x80x9copen transmission linkxe2x80x9d, i.e. this transmission link is not sheathed. Although the diffuse light conducted through this transmission link can then spread freely, the other transmission links are not influenced owing to their sheathing.
The system according to the invention offers the advantage that the advantages of an optical information transmission system, such as low susceptibility to faults, full-duplex operation and, in the case of a multi-channel execution, a real time application option can be utilized optimally by the use of economical receiver or transmitter devices. With the spread of diffuse light in free space, the problem normally exists that without the use of expensive modulation processes, light can only be transmitted in one direction simultaneously without mutual interference. This is acceptable for applications for which it is sufficient to transmit the information content only slowly. However, for certain requirements, for example an application in cars, this is not acceptable, as here a swift exchange of information with real-time characteristics is important. This disadvantage is remedied by the transmission system according to the invention.
Infrared light (IR light) can be used as diffuse light, for example, but any other diffuse light is also suitable.
The use of IR light as an example of diffuse light makes it possible to use. Standard IrDA (Infrared Data Association) elements, such as infrared receivers or transmitter units and to manage in this case without electrical connectors, optical coupler devices or complicated optical plug-in systems. Here no costly type of light modulation, such as phase shift keying, frequency or polarization modulation is necessary; the information is instead transmitted simply by the normal states xe2x80x9clight onxe2x80x9d and xe2x80x9clight offxe2x80x9d (on-off keying). Known procedures can be used as the transmission protocol.
A further advantage of using IR light consists in the fact that the system can operate as a genuine xe2x80x9creal-timexe2x80x9d system, i.e. only minimal conflict times occur (latency). Furthermore, a bus transfer is possible which permits simultaneous access by several users to the bus system (simultaneous multi user access).
Since when using infrared light no electrical fields of any kind are produced and the system is also insensitive to such fields, it is ideal for use in a sensitive environment. Furthermore, it is immune to shocks, vibrations and the respective surroundings. It thus has an extremely low susceptibility to faults in relation to condensation, dust, UV radiation etc.
The subsystems used can be any units communicating with one another, for example processors, and also devices such as mobile telephones, TVs, navigation units or graphics units, audio/video units and remote control systems.